In monitoring the blood pressure of a patient, it is customary to insert a catheter into an appropriate point in his circulatory system and couple the blood pressure so obtained into the hollow of a pressure dome. The hollow is closed by a flexible membrane that is maintained in intimate contact with the diaphragm of a transducer. As the blood pressure varies, the membrane moves the diaphragm of the transducer and causes corresponding variations in a blood pressure signal.
Previous pressure domes have been attached to the transducer by screw threads or other means whereby the contact pressure between the membrane of the dome and the diaphragm of the transducer depends on the applied torque. This produces a proportional offset in the blood pressure signal. If the pressure dome is attached too tightly, it may produce an offset that cannot be accommodated by the associated monitoring equipment, but, if the dome is attached too loosely, it may leak, causing errors in the blood pressure signal. Furthermore, when the pressure dome is replaced, it is usually necessary to rezero the monitoring equipment because it is unlikely that the contact pressure between the membrane of the new done and the diaphragm of the transducer will be the same as before. Variations in temperature may also alter the blood pressure signal.